Projection printing systems for forming an image on a light sensitive substrate or wafer normally include a mask having a transparent substrate with a pattern of opaque and transparent areas formed on one surface thereof, an illumination system for directing a beam of radiation energy such as light or UV rays through the mask to a radiation sensitive substrate or wafer, optical means for forming a focused image of the mask pattern on the radiation sensitive substrate and a pellicle cover for maintaining the images of any dirt particles on the surface of the mask out of focus. The pellicle cover is normally bonded to the substrate and completely covers the mask pattern. Such systems, for example, are described in U.S. Pat. Nos. 4,063,812 and 4,131,361 and in an article by Ron Hershel entitled: "Pellicle Protection of Integrated Circuits (IC) Masks", appearing in SPIE, vol. 275 Semiconductor Microlithography V1, (1981) page 23.
With increasing miniaturization, the pattern elements have become smaller and smaller to the extent that pattern resolution is limited by the wavelength of the light. This has led to the use of shorter wavelengths of the UV spectrum.
One disadvantage of the mask covers used heretofore is that they are only suitable for use in the range of from 4000 angstroms and above. Thus, an object of this invention is to provide a new and improved method of making a pellicle cover, which is suitable for use in the 2000 and 3000 angstrom range.